A single photon detector (hereinafter “SPD”) provides the ultimate limit of extremely weak electromagnetic radiation detection in term of sensitivity. Compact solid-state SPDs are regarded as enabling components in a wide range of applications such as biophotonics, tomography, homeland security, non-destructive material inspection, astronomy, quantum key distribution, and quantum imaging. Despite the astonishing progress of these fields in recent years, there has been little progress in the performance of SPDs, and thus the SPD is quickly becoming the “bottleneck” in these fields. Some of the important shortcomings of the current SPDs are: poor quantum efficiency, high dark count rates, lack of imaging arrays, severe cooling requirement for longer wavelengths, and large dead-times (low bandwidth) due to after-pulsing. Unfortunately, these problems become much more significant for wavelengths beyond visible range where a large number of applications can benefit the most. In particular, these drawbacks have prevented demonstration of the much-needed high-performance SPDs beyond the visible wavelength, and high-performance arrays of SPDs. Many applications can drastically benefit from two-dimensional imaging arrays of SPD, and SPDs that can operate in the longer wavelengths including: infrared mammography [2, 3], infrared tomography [4], molecular infrared florescent imaging [5-7], quantum imaging [8-10], infrared non-destructive inspection [11, 12] and remote detection of buried landmines [13-15].
There has been a rapid growth in research on SPDs, evident by an exponential increase in the number of related published papers over the past decade [1]. However, most of the works on compact solid-state SPDs have been focused on Geiger mode avalanche photodetectors (hereinafter “APD”) [16-19]. There are inherent drawbacks in the avalanche process that hinder realization of short and mid-infrared SPDs, as well as high-performance 2D SPD arrays. Some of these inherent physical limitations are:                Material Limitations: Almost all compound semiconductors that can provide longer wavelength detectors have a low ionization ratio, and subsequently a poor performance.        High Tunneling and Generation Rates: High electric filed leads to a high tunneling rate, even in the wide bandgap material, and tunneling current becomes the main source of the dark counts in modern APDs [19]. Also, the fully depleted avalanche region produces the maximum Shockley-Read-Hall (hereinafter “SRH”) generation noise [20].        Poor Uniformity: A fraction of a percent variation in doping or layer thickness can result in significant shifts in gain, dark current, breakdown voltage, and frequency response [21]. Temperature and bias variations would prevent realization of a uniform large-area 2D array.        High Photon Emission: The energetic (hot) carriers that are required for avalanche process can also produce photons. In fact, avalanche detectors are known to produce “photon flashes” that are three to four orders of magnitude brighter than the incoming beam. The produced photons can severely interfere with the other components of the system in a single element SPD [22], and produce a significant crosstalk in an arrayed SPD [23].        
These problems have encouraged research on alternative detection methods such as superconductor-base infrared detectors [24, 25], and quantum dot infrared detectors [26, 27]. Although these methods can potentially alleviate a large number of problems associated with avalanche-based SPDs, they require extremely low operating temperatures, about 4° K., which prevent their practical utilization in many applications. Quantum dot SPDs should be able to operate at much higher temperatures. However, their low quantum efficiency remains a serious problem. This is an inherent problem, and a consequence of the extremely small dimension of quantum dots compared with the wavelength of the infrared light.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.